Move _convert_to_nsx_transport_zones into nsx_utils

This routine does not need to be in the plugin class. This patch
transforms it into an utility method and adds unit tests to
increase coverage.

Change-Id: Ieacc36e729c4db90efd33944f7cf05dcb30e1de9
Closes-Bug: 1340210
NSX: Optionally not enforce nat rule match length check

This patch adds the 'raise_on_len_mismatch' parameter to the
'delete_nat_rules_by_match' function. The plugin then leverages
this parameter for ensuring NAT rules deletion operations
are completed successfully even when duplicate rules are found
or no corresponding rules are found at all.

With this change, the 'remove_router_interface' operation will
correctly complete even in cases when NAT rules in Neutron and
the NSX backend are out of sync.

This patch also changes a check in delete_nat_rules_by_match in
order to make it less expensive.

Closes-Bug: 1328181

Change-Id: I856d67ef5ff6264374cb8f2569668da4c205ad9f
Merge "Move _convert_to_nsx_transport_zones into nsx_utils"
Merge "NSX: Optionally not enforce nat rule match length check"